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such as letters, digits or spaces. The empty string is the special case where the sequence has length zero, so there are no symbols in the string. There is only one empty string, because two strings are only different if they have different lengths or a different sequence of symbols. In formal
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In this way, there could be multiple empty strings in memory, in contrast with the formal theory definition, for which there is only one possible empty string. However, a string comparison function would indicate that all of these empty strings are equal to each other.
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Even a string of length zero can require memory to store it, depending on the format being used. In most programming languages, the empty string is distinct from a
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The empty string is usually represented similarly to other strings. In implementations with string terminating character (
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or plain text lines), the empty string is indicated by the immediate use of this terminating character.
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to produce the empty string is known as an ε-production, and the symbol is said to be "nullable".
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There are two ways to create "empty strings" in R; the other is listed here as
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Corcoran, John; Frank, William; Maloney, Michael (1974). "String theory".
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The empty string is a syntactically valid representation of
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Formally, a string is a finite, ordered sequence of
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